A polycarbonate resin (hereinafter optionally referred to as PC resin) is excellent in mechanical strength (particularly, impact strength properties), electric properties, transparency and the like and widely used as an engineering plastic in such fields as office automation equipments, electric and electronic fields, automotive fields, construction and building fields and others. Such polycarbonate resin has a high limiting oxygen index among various thermoplastic resins and belongs to a resin generally bearing self-extinguishing properties so that it is utilized in a field demanding a high level of flame retardancy such as office automation equipments, electric and electronic equipments and others.
As described above, the PC resin is widely used in optical materials and the electric and electronic field and others, but difficult to recycle from the optical materials and others to a product with a similar quality including a recovery method so that its reuse is generally limited to cabinets and others. This is due to contamination by impurities and a decrease of a molecular weight by hydrolysis during recovery. Removal of impurities is also difficult and particularly in the case of optical materials, metal film adhesion and contamination by lubricants require a stringent treatment condition in washing and peeling to separate the PC resin, making it difficult to prevent the molecular weight from decreasing without choosing an appropriate condition.
A method to peel with an acid or a base (for example, see Patent Document 1), a mechanochemical method or a grinding method (for example, see Patent Document 2) and a blasting method are well known as a method for recycling and utilizing the PC resin used in CD, MD and the like. However, these methods may allow application of the recycled PC resin to cabinets and others, but are not practiced in recycling to a flame retardant material.
Many techniques are also proposed for a recycling system to supply recycled plastics giving stable quality to the recycled products (for example, see Patent Documents 3 and 4), but every one has a step to separate and recover, a step to crush the discarded optical discs that are separated and recovered and a step to isolate only the PC resin fragments from the crushed PC resin fragments, and in particular, Patent Document 3 is characterized with inclusion of a step to assure their quality, but these processes are not limited to plastic products, but easily known by analogy to a general recycling system existing long before in recycling of used paper, empty cans and the like and also Patent Documents 3 and 4 do not specifically disclose a separating method.
Of course, there is proposed decomposition of a PC resin under a supercritical condition down to a monomer such as 2,2-bis(4-hydroxyphenyl)propane (bisphenol A) and others as a raw material, but polymerization of such monomers to the PC resin again requires a higher cost and increases an environmental load because of higher consumption of energy.
Patent Document 1: Japanese Patent Laid-Open Publication No. H7-286064
Patent Document 2: Japanese Patent No. 323600
Patent Document 3: Japanese Patent Laid-Open Publication No. H2003-231120
Patent Document 4: Japanese Patent Laid-Open Publication No. H2004-74507